Apparatus for high speed manifolding of honeycomb structures

ABSTRACT

The invention is a flexible mask for use in charging a flowable material into selected cells of a honeycomb structure and is of particular utility in charging a sealing material into the ends of selected cells of such a structure during fabrication of solid particulate filter bodies and other selectively plugged honeycomb structures. The mask has a central body with a set of openings extending therethrough which allow passage of the flowable material through to the selected cells and a second set of protrusions extending from one of the surfaces of the mask which are used to align the mask to the end face of the structure and which extend into and sealably cover the cells which are not to receive the flowable material. The mask may be formed from a polymer, preferably an elastomer, using any of three disclosed die apparatuses. The mask may be used by fitting it to an end face of the structure and charging the flowable material through its openings or by fitting the mask across the orifice of an appropriate charging device, such as a ceramic cement press, and bringing the structure to the mask for fitting and charging.

This is a division of application Ser. No. 283,734, filed July 15, 1981,now U.S. Pat. No. 4,411,856.

BACKGROUND OF THE INVENTION

This invention relates to charging flowable materials into selectedcells of a honeycomb structure and, more particularly, to a method andapparatus for selectively manifolding (i.e., plugging) cells of ahoneycomb structure for the fabrication of filter bodies and otherselectively sealed honeycomb structures.

Honeycomb structures having transverse cross-sectional cellulardensities of approximately one-tenth to one hundred cells or more persquare centimeter, especially when formed from ceramic materials, haveseveral uses, including solid particulate filter bodies and stationaryheat exchangers, which require selected cells of the structure to besealed by manifolding or other means at one or both of their ends. Theterm "sealed" and its other corresponding grammatical forms (i.e.sealant, sealing, etc.) are used herein to refer to both porous and nonporous means of closing the open transverse cross-sectional areas ofcells.

It is well known that a solid particulate filter body may be fabricatedutilizing a honeycomb structure formed by a matrix of intersecting,thin, porous walls which extend across and between two of its opposingend faces and form a large number of adjoining hollow passages or cellswhich also extend between are are open at the end faces of thestructure. To form a filter, one end of each of the cells is sealed, afirst subset of cells being sealed at one end face and the remainingcells being sealed at the remaining opposing end face of the structure.Either of the end faces may be used as the inlet face of the resultingfilter. The contaminated fluid is brought under pressure to an inletface and enters the body via those cells which have an open end at theinlet face (i.e., "inlet" cells). Because these cells are sealed at theopposite end face ("outlet" face) of the body, the contaminated fluid isforced through the thin, porous walls into adjoining cells which aresealed at the inlet face and open at the outlet face (i.e., "outlet"cells). The solid particulate contaminant in the fluid which is toolarge to pass through the porous openings in the walls is left behindand a cleansed fluid exits the filter body through the outlet cells foruse.

Rodney Frost and Irwin Lachman describe in a copending application Ser.No. 165,646, filed July 3, 1980 and now abandoned, entitled FILTER ANDRELATED APPARATUS and assigned to the assignee of this application, amost efficient solid particulate filter body formed from a honeycombstructure in which the cells are provided in transverse, cross-sectionaldensities between approximately one and one hundred cells per squarecentimeter with transverse, cross-sectional geometries having nointernal angles less than thirty degrees, such as squares, rectangles,equilateral and certain other triangles, circles, ellipses, etc. Thecells are also arranged in mutually parallel rows and/or columns.Alternate cells at one end face are filled in a checkered orcheckerboard pattern and the remaining alternate cells are sealed at theremaining end face of the structure in a reversed pattern. Thus formed,either end face of the filter body may be used as its inlet or outletface and each inlet cell shares common thin, porous walls with onlyadjoining outlet cells, and vice versa. Other cellular cross-sectionalgeometries and other patterns of sealed cells may be employed tofabricate effective, although perhaps less efficient filter bodies thanthose of Frost and Lachman.

For the mass production of such filters, it is highly desirable to beable to seal selected cell ends as rapidly and as inexpensively aspossible. Frost and Lachman in the previously referred to applicationSer. No. 165,646 and now abandoned describe fabricating filter bodies bymanifolding (i.e., plugging) the end of each cell individually with ahand-held, single nozzle, air actuated gun. The hand plugging ofindividual cells by this process is long and tedious and is not suitedfor the commercial production of such filters and other honeycombstructures which may have thousands of cells to be selectively sealed.Frost and Lachman also postulate the use of an array of nozzles so thatthe sealing material may be simultaneously injected into a plurality orall of the alternate cells at each end face of the honeycomb structure.However, a working model of this device is not known to exist forplugging honeycomb structures having these higher cell densities.

In a copending application Ser. No. 283,733, filed July 15, 1981,entitled IMPROVED METHOD AND APPARATUS FOR SELECTIVELY CHARGINGHONEYCOMB STRUCTURES and assigned to the assignee of this application,Rodney Frost and Robert Paisley first describe the use of a mask havinga number of openings extending through it for selectively manifoldinghoneycomb structures in the fabrication of solid particulate filterbodies. Their embodiment was a rigid plate having a number of bores.

Masks have also been formed for manifolding cells which are regularlyinterspersed among substantially mutually parallel rows andsubstantially mutually parallel columns at an open surface of ahoneycomb structure by applying strips of an adhesive backed flexiblewebbing impermeable to the sealing material, such as masking tape, overselected rows and columns of cells or, alternatively, by providing amatrix of spaced, overlayed strips of a resilient, impermeable andreusable material such as metal foil which are joined together andfitted, with or without an underlying gasket, over the open surface ofthe structure with the openings through the matrix and gasket, ifprovided, positioned opposite the cells to be charged. By providing ahoneycomb structure with cells arranged in mutually parallel rows andmutually parallel columns and covering alternate rows and alternatecolumns of cells with strips of a suitable flexible material such as themasking tape or the joined thin metal strips, the open ends of one-halfof a subset of cells arranged in a checkered pattern across the end facewere exposed. After filling the ends of these cells, the strips wereremoved and strips applied covering the remaining alternate rows andremaining alternate columns thereby exposing the open ends of theremaining half of the subset of cells of the checkered pattern at theend face for filling. Both embodiments provide greater flexibility indealing with surface height variations and better masking of the cellends not to be charged including those which may be damaged than doesthe rigid plate embodiment. However, both embodiments must be appliedtwice to each end face to manifold all alternate cells at the end facein the desired checkered pattern of Frost and Lachman. This is asignificant limitation with respect to the tape strips which must beindividually applied across each end face, a time consuming task. Thereusable matrix and gasket of the second embodiment may be more quicklyapplied and removed, but like the rigid plate embodiments, is lesseasily adapted to distortions in the cell locations at the end faces.

In another embodiment, a rigid plate was provided with a plurality ofbores extending therethrough to register with the open ends of alternatecells of a honeycomb structure. Each bore was fitted with a shortfilling tube which protruded from the face of the plate and into a cellwhen the plate is aligned over the open cell ends of a honeycombstructure. A sealing material was forced from the opposing face of theplate through the bores into the cell ends receiving the tubes. To someextent, the filling tubes of the first embodiment assisted in aligningthe metal plate with the cells to be filled and reduce the likelihood ofsealing material being fed into the remaining cell ends covered by theplate. This embodiment was essentially inflexible, a limitation whichbecame more significant when cell densities in the honeycomb structurewere increased and distortions in the locations of cell walls becomerelatively more severe. Its rigid construction also sometimes damagedbrittle honeycomb structures.

In another embodiment, rigid rivets were attached at regular intervalsalong lengths of thin flexible strips and run along alternate diagonalsof cells arranged in mutually parallel rows and mutually parallelcolumns, each rivet being inserted into and covering the open end of acell along the diagonal. In this way, half of the cells exposed at anend face of the honeycomb structure were covered in a checkered or acheckerboard pattern and the open ends of all of the remaining cellsfilled in a single sequence of steps. The strip-backed rivets were moreflexible but required more handling than either of the plateembodiments, lessening their appeal for use in selectively charginghoneycomb structures on a commercial basis.

In copending application Ser. No. 283,732, filed July 15, 1981 now U.S.Pat. No. 4,557,773 and entitled IMPROVED METHOD AND RELATED APPARATUSFOR SELECTIVELY MANIFOLDING HONEYCOMB STRUCTURES, Roy Bonzo describesmanifolding the cells of a honeycomb structure by blocking off the openend faces of the structure with a solid covering applied thereto,preferably a preformed, transparent polymer film, and preferably anadhesive backed polyester film, and forming openings through thecovering opposite selected cells at each end face with a suitable tool.In the case of the polyester film, one or more heated probes which meltopenings through the film can form the openings. Again due to cellulardistortions, the number of probe elements which can be usedsimultaneously on an opening-forming tool and thus, the number ofopenings which can be formed by each application of the tool is limited.These indicated shortcomings of the existing art as well as otherproblems are overcome to various degrees by the subject invention.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved apparatus formore quickly sealing the cell ends of honeycomb structures in desiredpatterns so as to form solid particulate filter bodies and otherselectively manifolded honeycomb structures.

Other objects of the invention are that the apparatus be inexpensive tofabricate, easy to use, and reusable.

It is still another object of the invention to provide an apparatuswhich enables more uniform filling depths than were formerly achievedwhen charging plastically formable materials into selected cells of ahoneycomb structure using other mask embodiments.

It is yet another object of the invention to provide a selectivemanifolding apparatus which will not damage the cells of brittlehoneycomb structures, such as those formed from sintered materials, withwhich it is used.

It is yet another object of the invention to provide an improvedapparatus for fabricating solid particulate filter bodies and otherselectively sealed honeycomb structures using green (i.e. dried but notsintered) ceramic-based structures.

It is yet another object of the invention to provide an apparatus forselectively sealing honeycomb structures which is adaptable to automatedproduction.

These and other objects are satisfied by one aspect of the invention, amask, which is fitted over an open surface of a honeycomb structure andexposes the open ends of selected cells at that surface. The maskconsists of a central body having a first set of openings extendingbetween and through a pair of its outer faces and a second set ofprotrusions extending outwardly from one of the outer faces. The maskand its protrusions are flexible and preferably elastic. The protrusionsand openings are sized and spaced from one another so that when theouter face of the mask carrying the protrusions is applied to an opensurface of a honeycomb structure the openings expose cell ends selectedto be charged and the protrusions communicate with and extend into cellends not to be charged. The relative spacing of the openings andprotrusions on an unstretched, elastic mask are approximately the sameas or less than the spacing between the corresponding cell ends withwhich each is to coincide. The protrusions are preferably tapered froman outer diameter equal to or greater than the minimum inner diameter ofthe cells to an outer diameter less than that minimum inner diameter asthey extend away from the mask body so as to fill and temporarily sealcell ends into which they extend. In a mask embodiment for forming solidparticulate filter bodies having cells sealed in a desired checkered orcheckboard pattern, the openings and protrusions are arranged inalternating, mutually parallel rows across a face of the mask.

It is yet another object of the invention to provide means for formingsuch flexible masks.

It is yet another object to provide means for forming such elasticmasks.

These and other objects are satisfied by a second aspect of theinvention which are apparatus for forming the subject masks. In a firstdie embodiment, a die piece is provided with a mask forming surface anda number of openings extending through the mask forming surface andthrough the die piece which form the protrusions of the mask. A cavityis formed around the openings and extending away from the mask formingsurface to mold the mask body. Typically, the die piece is constructedby attaching to an outer surface of a first plate having a number ofbores extending through it, a second plate having an central cutoutwhich forms the cavity sidewalls. A selected formable mask material,preferably an elastic polymer, is loaded into the die piece and aftersolidifying, the formed mask is removed from the die. Openings areformed through the mask at selected locations by suitable means such asdrilling. In a second embodiment, a number of opening forming means suchas pins are provided on the mask forming surface of the die piece of thefirst embodiment, the pins protruding upwardly through the cavity inwhich the mask body is formed. The mask is fabricated as with the firstembodiment with the opening forming means creating openings through themask being formed. A third embodiment, a compound die apparatus isprovided having a first die piece with a number of openings extendingtherethrough for forming protrusions in the flexible mask, a second diepiece having a number of opening forming means such as pins extendingfrom one of its outer surfaces, the two die pieces being positionedtogether with the opening forming means contactably mating with an outersurface of the first plate, and a third stripper die piece having anumber of openings through it which allow the stripper to be slidablymoved along the opening forming means into contact with the second diepiece. The length of the opening forming means is greater than thethickness of the third die piece and causes a cavity to be createdbetween the first die piece and third stripper die piece, in which themask body is formed. A suitable material such as an elastomer isintroduced into the cavity. After solidifying, the first die piece isremoved and the stripper die piece is separated from the second diepiece removing the mask from the opening forming means.

Yet another aspect of the invention is a device for charging a flowablematerial into selected cells of a honeycomb structure. A feed head isprovided having an exit orifice and a subject flexible mask is fittedacross the orifice with its protrusions extending outward from the headand orifice. A honeycomb structure is fitted to the mask for chargingwith a flowable material passing through the feed head and maskopenings.

DETAILED DESCRIPTION OF THE DRAWINGS

The various aspects of the invention are better understood withreference to the accompanying drawings, in which:

FIG. 1 is a perspective, schematic view of the subject flexible mask anda honeycomb structure with which it is used;

FIG. 2 is an end face schematic view of the subject flexible mask ofFIG. 1 showing the relative positioning of some of its adjoiningopenings and protrusions;

FIG. 3 is a sectioned view of the subject flexible mask being fitted toan end face of the honeycomb structure;

FIG. 4 is a greatly expanded and sectioned schematic view of the maskfitted to the end face of the honeycomb structure;

FIG. 5 is a schematic view of a solid particulate filter body formedusing the mask and honeycomb structure of FIGS. 1 through 4;

FIG. 5a is a sectioned view of the filter body of FIG. 5 along lines5a-5a,

FIG. 6a is a sectioned schematic view of a simple die for casting aflexible mask having protrusions but no openings;

FIG. 6b is a sectioned schematic view of the mask formed on the simpledie depicted in FIG. 6a having openings being formed through it;

FIG. 7a is a sectioned schematic view of a second simple die for forminga flexible mask having both protrusions and openings, showing a polymerbeing loaded into the die;

FIG. 7b depicts the upper surface of the polymer cast into the secondsimple die of FIG. 7a being smoothed to form an outer surface of aflexible mask;

FIG. 7c depicts schematically the curing of the mask in the secondsimple die in an oven;

FIG. 7d depicts schematically the flashing being removed from the lowerouter surface of the second simple die after the mask has been cured;

FIG. 7e depicts a sectioned, schematic, profile view of the maskproduced in the second simple die by the steps depicted in FIGS. 7athrough 7d;

FIG. 7f depicts schematically the undersizing of the mask with respectto the cells of the honeycomb structure;

FIG. 8a is an exploded schematic view of a compound mask forming dieapparatus;

FIG. 8b is a sectioned profile view of the compound die apparatus ofFIG. 8a in an assembled form;

FIG. 9 is a sectioned, schematic view of a press apparatus for charginga plastically formable material such as a plugging cement into ahoneycomb structure using the subject flexible mask; and

FIG. 10 is a schematic, sectioned view of an envisioned press apparatushaving a subject flexible mask incorporated into its exit orifice.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts an exemplary mask apparatus 20 and a honeycomb structure21 with which it is used for forming a solid particulate filter body inwhich the cells 27 are sealed in a checkered pattern as indicated inFIG. 5. The mask 20 consists of a body 22, having a pair of opposing,typically planar, outer surfaces 23 and 24 (see FIGS. 2-4). A number ofopenings 25 extend through the body 22 between and through the opposingouter surfaces 23 and 24. A number of protrusions 26 extend from thedownstream face 24 of the mask 20. The central longitudinal axes of theopenings 25 and protrusions 26 are typically normal to those surface 24although it is possible and in certain situations may be desirable tohave the openings 25 incline in a uniform direction with respect to thesurface 24. When the mask 20 is applied to an end face 28 or 29 of ahoneycomb structure 21, the openings 25 allow a sealant or otherflowable material to pass through the mask 20 into those cells 27 of thehoneycomb structure 21 opposite each opening 25. Again, the protrusionsare typically normal to the surface 24 but may be inclined, if desiredor required, with respect to that outer surface 24.

The honeycomb structure 21 has a large number of adjoining hollowpassages or cells 27 which extend in a substantially mutually parallelfashion through the structure between its end faces 28 and 29 (hidden).The end faces 28 and 29 typically are substantially square orperpendicular to the central longitudinal axes of the cells 27 but maybe inclined thereto if desired or required. In such case the protrusionsmust be comparably angled so as to fittable engage the cells and allowthe mask to sit flush to the end face. The cell axes desirably alignsubstantially with those of the protrusions 26 and openings 25, makingfitting of the mask 20 to the end faces 28 and/or 29 easier, and themask directs the flowable material passed through the openings 25directly into the cells for uniform filling across the cross-sections.The cells 27 are formed by a matrix of thin, intersecting walls 30 whichextend across and between the end faces 28 and 29. For solid particulatefilter bodies, the walls 30 are also porous and continuous across andbetween the end faces 28 and 29. The structure 21 may also be providedwith an outer skin 31 between the end faces 28 and 29 surrounding thecells 27.

A honeycomb structure 21 may be provided from any of a variety ofsuitable materials including metal, ceramics, glasses, paper, cloth andnatural or man-made organic compounds, as well as combinations thereof,by any method suitable for the materials selected. For the production ofsolid particulate filter bodies, porous walled honeycomb structures maybe conventionally formed by extrusion from sinterable mixtures in themanner described in U.S. Pat. Nos. 3,919,384 and 4,008,033. Cordieritecompositions preferred for forming substantially thermostable ceramichoneycomb structures with various degrees of open porosity are describedin the aforesaid Frost and Lachman application Ser. No. 165,646 and nowabandoned which is incorporated by reference herein in its entirety. Itwill be appreciated that a that a subject mask however, may be used withhoneycomb structures 21 formed from other materials and/or by othermethods.

The open, transverse cross-sectional areas of the cells 27 are squareand are arranged at the end faces 28 and 29 in mutually parallel rowsand mutually parallel columns which are mutually perpendicular to oneanother. It will be appreciated that the rows and columns may not beexactly parallel and perpendicular due to manufacturing limitations infabricating the honeycomb structure 21. The square, cross-sectionalgeometry and the row and column arrangement of cells at the end facesdepicted in this application are exemplary. A mask 20 may be fabricatedto fit a variety of cellular arrangements and cellular cross-sectionalgeometries and to provide a variety of selected cell charging patterns.

The positioning of the openings 25 in an protrusions 26 on the mask 20are made with respect to the cells 27 of the honeycomb structure 21 withwhich the mask is used. Each opening 25 is positioned on the mask tocoincide with the open end of a cell to be charged with a fillingmaterial through the mask when the mask is properly positioned over theend face (see FIG. 4). The openings 25 are suitably sized to expose theopen ends of the selected cell or cells sufficiently for charging butnot so large as to expose part or all of any other cell not to becharged. Larger openings can be provided to expose several adjacentcells if desired.

Each protrusion 26 is similarly positioned on the mask to suitablyengage and is preferably sized to seal a single cell at the end face 28or 29 over which the mask 20 is fitted. The protrusions 26 arepreferably elastic and taper from a diameter at their base which isequal to or larger than a diameter at their tip which is smaller thanthe minimum cross-sectional diameter of the open end of cell with whichthey engage. Cone-topped cylindrical protrusions depicted in FIGS. 1-4are easy to form as are other shapes having a surface of rotation (i.e.cones, domes, domed cylinders, bullet shapes etc). The protrusions neednot taper along their entire length although it is desirable that theprotrusion tip distal to the mask body 22 be tapered to provide sometolerance during initial registration of the protrusions with the cellends. The included angle of taper T between the protrusion side walls 33(see FIG. 4) near the distal tip of the protrusion 26 should be lessthan 90 degrees and desirably between approximately 10 and 50 degrees.

The mask 20 is formed from a flexible material impermeable to andnon-reactive with the sealing material or other flowable material to becharged through the mask 20. Flexibility allows the mask 20 to conformto unevenness and some distortions and deformities in the cellulararrangements at the structure's end faces 28 and 29. This characteristicis significant because in many cases, notably the ceramic arts,undistorted and undeformed honeycomb structures cannot be provided withregularity by conventional manufacturing techniques. This problemincreases with increasing cell densities, increasing end face dimensionsand decreasing structural stiffness during formation of the structure,and is relatively significant with respect to a mass fabrication ofceramic-based filter bodies such as the diesel particulate filterembodiment described in the aforesaid Frost and Lachman application Ser.No. 165,646 and now abandoned. Preferably the mask and its protrusionsare also elastic. Such masks are most conveniently formed monolithicallyfrom any of several possible elastomers (i.e., elastic polymers) bycasting or injection molding in a manner to be later described. Elasticmasks have been successfully formed from various silicones and urethanealthough it is envisioned that other flexible materials including otherelastic polymers may be used. Elasticity also allows the mask 20 andprotrusions 26 to accomodate cellular spacing distortions at the endfaces 28 and 29 and the tapered protrusions to sealably fit the openends of cells 27 without damaging them when the mask 20 is applied. Itis envisioned that the flexible masks will be fabricated from any ofseveral moldable, polymerizable resins including silicones and urethanesor other materials also having a Durometer Shore A value ranging betweenapproximately 10 and 70 (See ASTM Standard D-1706) and a Young's (E)Modulus of approximately 30,000 psi (about 2110 kg./cm.²) or less,although a Young's Modulus in the range of approximately 500 to 3000 psi(about 35 to 211 kg./cm.²) is preferred for elastic masks used infabricating solid particulate filter bodies from the aforesaidceramic-based honeycomb structures.

The mask 20 depicted is sized to cover the open end faces 28 and 29 ofthe structure 21. Protrusions 26 are provided on the mask 20 to fitablyengage each cell which is not to be charged with a sealing materialthrough the mask. It should be appreciated that a protrusion need not beprovided for each cell which is not to be charged at the covered endface and that many of the protrusions 26 on the exemplary mask 20 ofFIGS. 1 through 4 could have been eliminated without detrimentaleffects. Indeed, because cells at the periphery of an end face may havepartial or reduced cross-sectional areas which will make fitting afull-sized protrusion difficult or impossible, it may also be desirablein some applications to reduce the surface area of the mask to less thanthat of the end faces allowing the cells at the periphery of the endface to be charged, or, if that is unacceptable, to eliminate theprotrusions at the outer edge of the mask. Similarly, in certainapplications it may also be desirable to omit openings through certainareas of the mask so as to leave two or more adjoining cells unplugged.

Care should be taken to account for any shrinkage which occurs in thefabrication of the mask. If a polymerizable resin is used, it willtypically experience shrinkage at a rate which will differ as theproportions of its components and the conditions under which it is curedare varied. Exact sizing of a mask to its honeycomb structure ispreferred as dimensional mismatch will make the fitting of the mask toan end face more difficult. It was observed that if maskopening/protrusion spacing were excessively undersized or oversized withrespect to the corresponding cell spacing, the elastic protrusions would"knuckle under" while an elastic mask was being pressed aginst the endface making fitting impossible. Some tolerance to elastic maskundersizing has been observed in applying masks approximately 0.125inches (3 mm.) thick and having protrusions about 0.125 inches (3 mm.)long and about 0.07 inches (about 1.8 mm.) thick, openings about 0.086inches (about 2 mm.) in diameter and a Young's Modulus of approximately3000 psi (about 211 kg/cm²) or less to honeycomb structures having celldensities of approximately 100 cells/sq.in. (about 15.5 cells/sq.cm.).For very small areas, approximately one-half inch (1.27 cm) in diameter,about 8 to 10% undersizing of the mask could be accommodated; atdiameters of about 4 inches (10.16 cm), about 4% undersizing of the maskcould be accommodated; at a diameter of approximately 6 inches (15.24cm), approximately 1% undersizing of the mask could be accomodated. Notolerance for elastic mask oversizing was observed although very minoroversizing (less than 1%) might be accomodated. It is believed thatapproximately 1% undersizing over a 6 inch diameter area could beaccomodated for other elasic masks (having a Young's Modulus of up toapproximately 10,000 psi (about 703 kg./sq. cm.)). Undersizing of themask to the structure is depicted in FIG. 7f with reference to thecenterlines 63 of adjoining protrusions 26 and the centerlines 64 of thecells 27 with which they engage.

FIG. 2 is a view of the outer surface 24 of the mask 20 shown in FIG. 1and depicts a portion of its openings 25 and protrusions 26. Theopenings 25 and protrusions 26 are alternated with one another alongrows and columns parallel or perpendicular to the line 3--3 so as tocoincide with the rows and columns of cells 27 at the end faces 28 and29. Each opening 25 and protrusion 26 of the mask 20 in FIG. 2 will bepositioned juxtapose one cell 27 when the mask 20 is applied to eitherend face 28 or 29. As the mask 20 has been fabricated to fit either endface 28 or 29 and expose in a checkered pattern the square cells of thehoneycomb structure 21, the openings 25 and protrusions 26 are formed inrows mutually parallel to the line 3a--3a. The line 3a--3a bisects a rowof evenly spaced protrusions 26. Rows of evenly spaced openings 25 andevenly spaced protrusions 26 are alternated with one another across themask surface 24 to either side of the row of protrusions bisected byline 3a--3a. These rows of protrusions 26 and openings 25 will alignwith the diagonals of the cells 27 when the mask 20 is fitted to the endface 28 or 29. If a plugging material is charged through the openings 25in the mask 20, the open ends of the cells 27 in an adjoining end face28 or 29 will be filled in a checkered or checkerboard pattern as isindicated in FIGS. 5 and 5a.

The mask 20 may be hand fitted to an end face 28 or 29 of a honeycombstructure in the manner depicted in FIG. 3. It is suggested that theprotrusions 26 at or near one outer edge of the mask 20 be fitted intocorresponding cells 27 near an edge of the end face. The mask may bemoved laterally for very short distances in a variety of directionsacross the end face and rotated in opposing directions to start theengagement of one or more of the protrusions with appropriate cells inthe end face. Other protrusions 26 are fitted into appropriatecorresponding cells in directions radiating from the initially alignedprotrusions as indicated by the arrows extending across the outersurface 23 of the mask 20 in FIG. 3. It is helpful to stretch anundersized mask and vibrate it slightly back and forth across the endface 28 or 29 during this process to align the protrusions 26 with theappropriate cell ends. Once it is sensed that the protrusions havealigned with underlying cells, the outer surface 23 of the mask ispressed down to insert the aligned protrusions into the cell ends. Thisprocess is continued until the mask 20 is fitted flush across the entireend face 28 or 29 of the structure 21.

A solid particulate filter body is formed by charging a flowable sealingmaterial through the openings 25 in the mask 20 into a subset ofalternate cells at one end face 28 or 29, removing the mask 20, applyingit or a comparable mask to the remaining end face of the structure 21with the openings 25 aligned over the remaining alternate cells andcharging the sealing material into those cells. The structure andsealing material may be cured or fired, if appropriate. Foam-typecordierite ceramic cements, which are compatible with the aforementionedcordierite structures and chargeable with the subject mask, aredescribed in a pending application Ser. No. 165,647 by Robert Paisley,entitled CERAMIC FOAM CEMENT, filed July 3, 1980, now U.S. Pat. No.4,297,140 reissued as Re. No. 31,405 and a preferred composition of thiscement is described in the aforesaid Frost and Lachman application Ser.No. 165,646. The application Ser. No. 165,647 is assigned to theassignee of this application and is incorporated by reference herein. Itis envisioned that the subject masks may also be used to chargenon-foaming ceramic cements as well as other flowable materials ofvarious viscosities into selected cells of honeycomb structures forvarious applications.

A filter body formed from the structure 21 of FIGS. 1 through 4 isdepicted in FIGS. 5 and 5a with alternate cells 27 sealed in a checkeredpattern on end face 28. This pattern is reversed on the end face 29 ascan be seen in part in FIG. 5a, a cross-sectioned view along a row ofthe cells in the filter body of FIG. 5 depicting the plugs 32 formed bythe sealing material charged through the mask openings 25. Flow of acontaminated fluid through the filter is indicted in FIG. 5a by arrows34. The contaminated fluid enters through the "inlet" cells 27 open atthe left ("inlet") end face 28, passes through the thin and porous walls30, into adjoining "outlet" cells open at the right ("outlet") end face29, and in the process leaves the contaminants too large to pass throughthe walls 30 in the inlet cells open at end face 28. Additionally theplugs 32 may be formed with open porosity equal to or less than that ofthe thin walls 30 and allow some fluid flow therethrough which will notimpair the operation of the filter body. Operation of the filter isdescribed in more detail in the aforesaid application Ser. No. 165,646.

A second aspect of the invention is die apparatus and methods for usingthe same to fabricate a flexible or elastic mask similar to thatdepicted in FIGS. 1 through 4. A first mask forming apparatus isdepicted in cross-section in FIG. 6a and consists of a mold 40 having amask forming outer surface 41, typically planar, and a multiplicity ofbores 42 extending through the mask forming surface 41 and mold 40 indirections essentially normal to the mask forming surface 41. A cavity44 in which the mask body is formed is defined by a ridge 43 whichextends outwardly from the mask forming surface 41. The bores 42 formthe protrusion 26 of the mask 20 and are desirably tapered inwardly asthey extend away from the mask forming surface 41, preferably at anincluded angle between approximately 10 and 50 degrees. After being castin a manner to be subsequently described, the mask is removed from themold 40 and openings 25 made through the body of the mask 20 at selectedlocations among the protrusions 26 as indicated in FIG. 6b. The openings25 may be made by any suitable means such as but not limited to boring,cutting, drilling (depicted), burning and melting. If formed from aelastic polymer, the mask may be chilled to make the operation easier toperform. In the preferred embodiment, the openings 25 are alsoessentially normal to the outer downstream surface 24 of the mask 20from which the protrusions 26 extend.

FIG. 7a depicts a cross-sectioned profile view a second mask formingapparatus. Like the first apparatus of FIG. 6a, the second apparatus ofFIG. 7a consists of a mold 50 having a plurality of tapered bores 52, amask forming surface 51, and a ridge 53 which forms with the maskforming surface 51 a cavity 54 within which the body of the mask isformed. The second apparatus further includes a plurality of means 55,such as pins, for forming an equal plurality of openings through themask. It is preferred that the tops of the means 55 form a common planewith the top of the ridge 53 to assist in forming a flat outer surfaceon the mask, as will be subsequently described.

A mask 20 formed within the apparatus of FIG. 7a is depicted incross-section in FIG. 7e and has a pair of opposing outer surfaces 23and 24, a first plurality of openings 25 extending through and betweenthe outer surfaces 23 and 24, and a second multiplicity of protrusions26 extending from the outer surface 24. Again, the protrusions 26 arepreferably tapered downward at an included angle of between about 10 and50 degrees and the protrusions 26 and the openings 25 extend essentiallynormally from the outer surface 24.

Simple working models of die apparatus corresponding to those depictedin FIGS. 6a and 7a through 7d can be formed from transversecross-sections of the honeycomb structures with which the masks are tobe used. To form the die of FIG. 6a, the cells of a honeycomb sectionare filled with an easily removed solid material such as wax and affixedto a supporting plate using wax or a suitable adhesive. The wax or othersolid material is removed from selected cells in which protrusions ofthe mask will be formed. The outer perimeter of the sectioned structureis then surrounded with a collar to form ridge 43 and a selected polymeris cast in the mold thus formed. A die apparatus similar to thatdepicted in FIGS. 7a through 7d may be formed by the additionalinsertion of pins into selected cells of the sectioned structure. AConap, Inc. No. TU-65 urethane was mixed according to directions andcast in such an apparatus to establish the feasibility of the castingprocesses. After a room temperature cure for about 18 hours, thesolidified mask was removed from the die and oven heated at about 200°Fahrenheit (93° Centigrade) for about 16 hours to complete curing.Preferably, however, the die apparatus is fabricated from a rigid,machinable material such as metal for precise dimensioning of the formedmask. It will further be appreciated that the die apparatus of FIGS. 6aand 7a through 7d can be constructed in two pieces consisting of a flatplate having a mask forming surface 41 or 51 with, in the latter case,openings forming means 55 protruding therefrom and bores 42 or 52extending therefrom and therethrough and a second plate having a centercutout which is attached to the first plate 40 or 50 to provide theridge 43 or 53 forming the cavity 44 or 54.

A mask is formed in the mold 50 in the manner depicted in FIGS. 7athrough 7d. The mold 50 is cleaned with a suitable agent such as acetoneor xylene prior to forming each mask. After cleaning the inner surfacesof the mask forming cavity 54 and bores 52, they are coated with asuitable releasing agent, such as a 20:1 ratio by weight solution ofmethylene chloride and Johnson™ Paste Wax. A suitable polymerizableresin ("polymer") is mixed and de-aired by an appropriate device such asa vacuum chamber. A mass of mixed and de-aired polymer 56 is applied totop of the mold 50 and is worked into the cavity 54 and bores 52 with asuitable tool 57 such as a spatula or putty knife. The mold 50 may bemounted on a vibrator platform 58 and/or a vacuum source 59 may beapplied to the ends of the bores 52 opposite the mask forming surface 51in order to work the polymer into the bores 52 and recesses of thecavity 54. Other devices such as ultrasound sources (not depicted) maybe employed in working the polymer into the cavity 54 and bores 52. Thesurface of the polymer is leveled with the upper surfaces of the ridge53 and opening forming means 55 with the tool 57. The extrusion of thepolymer material through all of the openings of the bores 52 at thebottom surface 61 of the mold 50 (see FIG. 7b) indicates that the cavity54 and bores 52 are filled. The tops of the means 55 then are scrapedclean with a sharp edge 60 such as a razor as depicted in FIG. 7b,leaving a smooth outer face on the molded polymer. The polymer is thencured in a manner appropriate for the materials selected. The curing ofmany polymers may be accelerated by baking as is depicted in FIG. 7c.After baking, the mold 50 and cured polymer are removed from the ovenand are allowed to cool. Once the mold 50 is sufficiently cooled to behandled, the polymer extruded through the bottom of the bores 52 andbeyond the bottom surface 61 of the mold 50 are removed by suitablemeans 62 such as a razor blade or scraper as indicated in FIG. 7d. Thecured polymer is then pulled from the mold and trimmed to an appropriatesize, if required. Except for the cleaning of the pin tops (FIG. 7b),the same steps are followed in casting a mask in the mold 40 (FIG. 6a).Again, openings must be formed through the mask after its removal fromthe mold 40 (FIG. 6b).

Yet another apparatus, an envisioned compound die for forming a mask, isdepicted in an exploded view in FIG. 8a and in a sectioned profile viewin FIG. 8b, and consists of a first die piece 65 having means 66 to formthe plurality of openings in the subject mask, a second die piece 67 forforming the flexible protrusions extending from one face of the mask anda third die piece 68 positioned between the die pieces 65 and 67 forstripping the subject mask from the die after being formed. Thiscompound die apparatus allows faster and easier mask fabrication thaneither of the die apparatus depicted in FIGS. 6a and 7a through 7d. Thefirst die piece 65 has an essentially planar bottom outer surface 69(hidden) from which extends a plurality of means 66 such as pins ortubes for forming the openings 25 in the mask 20 (see FIGS. 1 through4). The second die piece 67 has an upper outer surface 70 designed tocontactably mate with the ends of the means 66. For ease of use it issuggested that the ends of the means 66 be flat and form a common planeand that the outer surface 70 of the second die piece 67 also be planar.The second die piece 67 is further provided with a plurality of bores 71extending therethrough from the outer surface 70. The walls of the bores71, which form the protrusions 26 of the mask 20 (FIGS. 1 through 4),extend normally away from the outer surface 70 for a short distance andthen taper inwardly, suggestedly at an included angle of betweenapproximately 10 and 50 degrees as they extend away from the outersurface 70. The third die piece 68 is essentially planar and ispositioned within a cavity 72 formed between the first and second diepieces 65 and 67, respectively, when the opening forming means 66 arepositioned against the second piece outer surface 70 (see FIG. 8b). Thethird die piece 68 is provided with a second plurality of bores 73 equalto the number of means 66 and which are positioned and sized so as toallow the third die piece 68 to be slid along the means 66 andpositioned against the surface 69 of the first die piece 65 with themeans 68 extending completely through and protruding from lower surface74 of the third die piece 68. The tolerances between the plurality ofbores 73 and means 66 should also be sufficiently tight to prevent theintrusion of polymer and the formation of flash during the fabricationof the mask. However, if flash is formed it may be removed by suitablemeans such as water jetting or burnishing. The mask is formed betweenthe lower surface 74 of the third die piece 68 and upper surface 70 ofthe second die piece 67.

A mask may be cast in the third die apparatus in a manner similar tothat used with the first two die embodiments. The die pieces 65, 67 and68 are cleaned and a removal agent applied to the mask forming surfaces.A suitable polymer is mixed, de-aired and applied to the upper face 70of the second die piece 67 and is worked into the bores 71. The secondpiece 67 may be formed with a ridge 75 to contain the polymer duringthis process. The mated first and third die pieces 65 and 68 are pressedagainst the second die upper surface 70 and held in place by suitablemeans 76 such as clamps (depicted) or screws or nuts and bolts duringthe curing of the polymer. If the peripheral ridge 75 is provided, itshould be low enough so that one or more narrow gaps 77 are formedaround the cavity 72 through which excess polymer material may besqueezed (see FIG. 8b). The third die piece 68 is held against the firstdie piece 65 by the polymer between the piece 68 and the second diepiece 67. After curing, polymer extruded through the tapered bores 71 isagain removed by a suitable tool such as a razor knife (see FIG. 7d).The means 76 used to hold the three die pieces together are removed andthe second die piece 67 removed from the first and third die pieces 65and 68. Frictional forces will hold the mask 20 to the opening formingmeans 66 extending through the mask forming lower surface 74 of thethird die piece 68. This mask forming lower surface 74 eliminates theseparate upper mask surface forming step required in the first two dieembodiments (see particularly FIGS. 7a and 7b). The mask 20 thus formedwithin the cavity 72 and tapered bores 71 may be stripped from theopening forming means 66 by sliding the third die piece 68 along themeans 66 away from the first die piece 65. If desired or necessary, theformed mask may be trimmed to a suitable shape for use.

Comparable die pieces may also be used for injection molding of themask. In an injection molding apparatus, means are provided forinjecting the polymer or other flowable material into the cavity, suchas through the gap(s) 77.

Sintered honeycomb structures with which the described mask have beenused, typically experience shrinkage during their drying and sinteringcycles which vary with compositional and drying/curing schedulevariations. By varying polymer mixtures and/or curing schedules, theshrinkage and thus the relative dimensions of the flexible maskfabricated may also be controllably varied. In this way, a single dieapparatus may be used to fabricate different masks accomodatinghoneycomb structures experiencing slightly different shrinkages. Again,exact sizing of the mask to the structure is desired but to the extentthat that goal cannot be achieved, slight undersizing is preferred tooversizing. Several silicon formulations have been successfully castusing a die apparatus similar to that depicted in FIGS. 7a through 7dformed from machined brass plates incorporating steel, opening formingpins. In each case, the polymer components were mixed, deaired with anapproximately 28 inch (71.1 cm.) mercury vacuum for about 20 minutes,applied to the die apparatus and heated for about 8 to 10 minutes atabout 240° to 260° Centigrade to accelerate curing. After cooling andremoving from the die apparatus, some masks were subjected to anadditional post-curing cycle in which each was again heated atapproximately 230° to 250° Centigrade for about 16 hours. In each suchcase, post-curing yielded additional shrinkage. Silicone mixtures whichhave been successfully cast and their observed linear shrinkage fromoriginal die dimensions under the aforesaid oven curing and, whereindicated, post-curing schedules are as follows (all % are by volumeexcept where otherwise indicated).

    __________________________________________________________________________                                           ADDITIONAL                                                            CURE    POST-CURE                                                                              TOTAL                                                        SHRINKAGE                                                                             SHRINKAGE                                                                              SHRINKAGE                     POLYMER                        % (APPROX.)                                                                           % (APPROX.)                                                                            % (APPROX.)                   __________________________________________________________________________      Dow Corning Q3-9595 silicone resin (50%                                                                    3.0-3.3 0.5-0.8  3.8-4.0                         A component mixed with 50% B component)                                       Dow Corning Q3-9590 silicone resin (50%                                                                    2.3-2.6 1.4-1.7  about 4.0                       A component mixed with 50% B component)                                       Dow Corning Q3-9595 (50% component A mixed                                                                 2.8-3.0 0.8-1.0  3.8-4.0                         with 50% component B) mixed with additional                                   10% (by weight) Dow Corning X3-6596A sili-                                    cone resin (A component only)                                                 Dow Corning X3-9592 (50% A component mixed                                                                 2.5-2.8 0.7-1.0  3.2-3.5                         with 50% B component)                                                         50% (by weight) Dow Corning Q3-9595 B com-                                                                 2.8-3.0 about 1.0                                                                              3.8-4.0                         ponent silicone resin mixed with 50% (by                                      weight) Dow Corning X3-6596 A component silicone resin                        Dow Corning X3-6596 silicone resin (50% A                                                                  1.9-2.1 0.7-0.9  2.7-3.0                         component mixed 50% B component)                                              25% (by weight) Dow Corning Q3-9590 silicone resin                                                         2.2-2.4 1.0-1.2  3.5-3.7                         (50% A component mixed with 50% B component) mixed                            with 75% (by weight) Dow Corning X3-6596 silicone resin                       (50% A component mixed with 50% B component)                                  25% Dow Corning Q3-9590 silicone resin (50% A                                                              2.5-3.0                                          component mixed with 50% B component) mixed with                              75% Dow Corning X3-6596 silicone resin (50% A                                 component mixed with 50% B component)                                         90% Dow Corning Q3-9595 silicone resin (50% A                                                              2.5-3.0                                          component mixed with 50% B component) mixed                                   with 10% Dow Corning X3-6596 A component silicone resin                     10.                                                                             Dow Corning No. 732 silicone resin (50%                                                                    1.8                                              A component mixed with 50% B component)                                       Dow Corning No. 734 silicone resin (50%                                                                    1.8                                              A component mixed with 50% B component)                                     __________________________________________________________________________

Silicone oils have also been added to silicone resins to obtain evengreater shrinkages. In each case, the oil was mixed into a mixed siliconresin, de-aired, cast and heated in a mold through the aforesaid curingschedule (230° to 260° Centigrade for 8 to 10 minutes) but was subjectedto a post-cure baking at about 230° Centigrade for only about 4 hours.The mixtures examined and their cure, additional post-cure and totalshrinkages are as follows (all % are again by volume unless otherwiseindicated).

    __________________________________________________________________________                                          ADDITIONAL                                                            CURE    POST-CURE                                                                              TOTAL                                                        SHRINKAGE                                                                             SHRINKAGE                                                                              SHRINKAGE                      POLYMER                       & (APPROX.)                                                                           % (APPROX.)                                                                            % (APPROX.)                    __________________________________________________________________________      82.5% (by weight) Dow Corning X3-6596 silicone                                                            2.6-2.8 1.8-2.0  4.4-4.6                          resin (50% A component mixed with 50% B                                       component) mixed with 17.5% Dow 200 Silicone Oil 20CS                         90% (by weight) Dow Corning X3-6596 silicone                                                              2.4-2.7 0.6-0.8  3.1-3.5                          resin (50% A component mixed with 50% B component)                            mixed with 10% Dow 200 Silicone Oil 500CS                                   __________________________________________________________________________

Other ratios and curing schedules should yield a range of shrinkages. Atleast one silicone resin, Dow Corning 184, could not be cast on theaforesaid mold apparently due to interaction with the brass. Adversereactions may be encountered with other die material and polymer mixes.

Yet another aspect of the invention are methods and apparatus formanifolding selected cells of a honeycomb structure as would be doneduring the fabrication of solid particulate filter bodies, using theflexible, elastic masks heretofore described. An exemplary pressapparatus 80 is depicted in cross-section in FIG. 9. A flexible mask 20and honeycomb structure 21 are provided in the manner previouslydescribed. The mask 20 has been applied to an end face 28 of thehoneycomb structure 21 with its protrusions 26 and openings 25 alignedwith the ends of alternate cells 27 at the end face 28. Slightundersizing of the mask 20 will provide mechanical self-locking of it tothe structure 21. Moreover, it is suggested that a flexible tubularcollar 81 of a suitable material such as neoprene be stretch fitted overthe peripheral edges of the mask 20 and outer sidewall 31 of thestructure 21 adjoining the end face 28 to assist in holding the mask 20to the structure 21 and in sealing the structure 21 over an orifice 83on the upper face 94 of a press head 86. An adjustable, flexible clamp82 is provided around the collar 81 so as to better secure it to themask 20 and structure 21. The press apparatus 80 comprises the presshead 86 supported by a frame 88. The head 86 is equipped with a piston84 slidably mounted in a bore 85 for charging a cement mixture throughthe orifice 83 over which a honeycomb structure 21 is secured. Prior tocharging, the piston 84 is backed away sufficiently from face 94 to forma chamber above the piston head which is loaded through the orifice 83with a suitable amount of a ceramic cement such as the foam-type cementspreviously referred to. The mask 20 and structure 21 mounting the collar81 and clamp 82 are then placed over the orifice 83 and held in place bysuitable means such as a bar 89 placed across the remaining end face 29of the structure 21 and held into place by suitable means such as bolts90 extending through the bar 89 and into suitably threaded bores 91 ofthe press head 86. The piston 84 is then advanced towards the exitorifice 83 by means of a hand-operated screw 87 or other suitable meansand, in the process, presses the cement mass, above the piston 84,against the mask 20 and through its openings 25 into the proximal openends of the cells 27 juxtaposed to the openings 25, forming cement plugs92. During this step, the flexible collar 81 also seals thecircumferential edge of the orifice 83, preventing the cement from beingforced out past the end face 28. Similar plugs 93 have already beenformed in the ends of the remaining alternate cells 27 proximal the endface 29 in a previous filling. The structure 21 may then be removed fromthe press apparatus 80, and the flexible collar 81 and mask 20 may beremoved from the structure 21, which is ready for firing to sinter plugs92 and 93 and structure 21, if appropriate.

A preferred double headed cement press for simultaneously filling bothends of a honeycomb structure using a pair of the subject masks isdescribed in the copending Roy Bonzo application Ser. No. 283,732 nowU.S. Pat. No. 4,557,773. Where a pair of masks are used, they may beheld in place during handling of the honeycomb structure before itsinsertion into the press by providing undersized masks or by temporarilysecuring the masks to the end faces of the honeycomb structure with amild adhesive which will allow their easy removal after charging.

A preferred method for automatically fitting a subject flexible mask toa honeycomb structure end face is described in a second copendingapplication Ser. No. 283,735, filed July 15, 1981, and now abandonedwhich is assigned to the assignee of this application and incorporatedin its entirety by reference herein. The invention involves centering amask, such as that depicted in FIGS. 1 through 4, over an end face of ahoneycomb structure and preferably constraining its movement toapproximately one-half of a cell diameter or less in any lateraldirection while inputting a rotational vibrating motion to the structureor the mask. The mask will self-align in one of a limited number ofpredetermined locations.

It is further envisioned that the subject mask 20 may be fitted acrossthe feed orifice 101 of a filling device such as a cement press having apress head 100 as depicted schematically in FIG. 10 so as to feed aflowable material, in this embodiment a plastically formable cement,into a honeycomb structure fitted to the filling device's flexible mask20. The mask 20 is secured to the press head 100 by a suitable collar102 holding mask 20 against an annular plate 103 or other suitablemeans. The collar 102 is secured across the feed orifice 101 again bysuitable means such as threading 104 or fasteners (not depicted). Thestructure 21 is brought to the mask and fitted against its exposedprotrusions 26. Cement (shading) is fed into a cavity 106 formed in thepress head 100 between a piston 105 and the upstream face 23 of the mask20 through appropriate means such as feed tubes 107. The piston 105 isadvanced as indicated by arrow 108 and forces the cement against themask 20 and through its openings 25 into the open ends of the opposingsubset of cells 27. It is further envisioned for fabrication of solidparticulate filter bodies and other honeycomb structures manifolded atboth their end faces that a second press head similar to the head 100depicted be provided with an appropriate mask 20 for simultaneouscharging of both end faces of the structure.

While the subject invention has been described with particular referenceto the manifolding of honeycomb structures in the fabrication of solidparticulate filter bodies, it will be appreciated that it may be moregenerally employed in the loading of the plastically-formable or otherflowable substances into selected cells of a honeycomb structure.Moreover, the descriptions and suggested modifications of the variousaspects of the invention provided herein are intended to be merelyillustrative of rather than limiting the scope of the invention which isset forth more particularly in the following claims.

What is claimed is:
 1. A flexible mask for covering an open surface of ahoneycomb structure having a multiplicity of hollow cells, including asubset of said cells, extending therein from said open surface and withopen ends exposed at said open surface, comprising:a solid flexible bodyhaving a pair of opposing outer faces, a first one of said outer facesadapted to be applied to said open surface; a plurality of openingsextending through said body between and through said pair of opposingouter faces, said openings adapted to be aligned opposite the cells ofsaid subset; and a plurality of flexible protrusions extending from saidfirst one of the opposing outer faces and adapted for engaging an equalplurality of said open ends of the cells other than the cells of saidsubset.
 2. The mask of claim 1 wherein said body and said protrusionsare formed from materials having Durometer Shore A values ofapproximately 70 or less.
 3. The mask of claim 1 wherein said body andsaid protrusions are also elastic.
 4. The mask of claim 1 wherein saidbody and said protrusions have a Young's Modulus of approximately 10thousand pounds per square inch or less.
 5. The mask of claim 1 furtherbeing monolithic.
 6. The mask of claim 5 further being formed from anelastic polymer.
 7. The mask of claim 6 further being formed from asilicone, or urethane polymer.
 8. The mask of claim 1 wherein saidprotrusions are tapered.
 9. The mask of claim 1 wherein said protrusionsare arranged in a plurality of substantially mutually parallel rowsacross said first one of the opposing outer faces.
 10. The mask of claim9 wherein said openings are also arranged in substantially mutuallyparallel rows which are alternated with said rows of protrusions acrosssaid first one of the opposing outer faces.
 11. The combinationcomprising:a honeycomb structure having a multiplicity of hollow cells,including a subset of said cells, extending therein from an open surfacethereof and with open ends exposed at said open surface; and a flexiblemask applied to said open surface and comprising a solid flexible bodyhaving a pair of opposing outer faces, a first one of said outer facesapplied to said open surface, a plurality of openings extending throughsaid body between and through said pair of opposing outer faces, saidopenings aligned opposite the cells of said subset, and a plurality offlexible protrusions extending from said first one of the opposing outerfaces and engaging an equal plurality of said open ends of the cellsother than the cells of said subset.
 12. The combination of claim 11wherein said mask is elastic.
 13. The combination of claim 12 whereinsaid mask is stretched across said honeycomb surface.
 14. Thecombination of claim 11 wherein said open ends of said cells have asubstantially uniform minimum transverse cross-sectional diameter andsaid protrusions are tapered from a diameter equal to or greater thansaid minimum diameter to a diameter less than said minimum diameter. 15.The combination of claim 11 wherein said cells are arranged across saidopen surface in rows and said openings expose substantially allalternate cells of the multiplicity in a checkered pattern across saidopen surface.
 16. The combination of claim 11 wherein said honeycombstructure is formed from a mixture including ceramic materials.
 17. Thecombination of claim 16 wherein said mask is formed from an elasticpolymer.
 18. A mask for use in applying a filler material to plugalternate openings in an extruded ceramic monolith element during thefabrication of a particulate filter, the monolith element being of thetype having a continuous outer wall internally interconnected by a largenumber of interlaced thin porous internal walls defining parallelpassages extending longitudinally through the ceramic monolith elementfrom opposite end faces thereof with the passages being of substantiallyuniform cross section and arranged in vertical and horizontal rows whenviewed in elevation of a said end face thereof to define a honeycombmatrix; said mask, of flexible elastomeric material, includes a flatbase member of a size and shape complementary to a said end face wherebyit can be placed in abutment thereagainst, said base member having aplurality of flexible pins extending outward from one face thereof withsaid pins arranged in a checkerboard configuration, said pins being of asize and shape for insertion into alternate said passages, and having aplurality of apertures extending therethrough with said aperturesarranged in a checkerboard configuration but offset relative to saidpins, said apertures being of a size and shape whereby a filler materialcan be extruded therethrough into the associate aligned alternatepassages of the monolith element whereby to effect blocking of that endof said passages.
 19. A mask for use in the fabrication of a particulatefilter, the mask being used to apply a filler material to plug alternateopenings in an extruded ceramic monolith element of the type having acontinuous outer wall internally interconnected by a large number ofinterlaced thin porous internal walls defining parallel passagesextending longitudinally through the ceramic monolith element fromopposite end faces thereof with the passages being of substantiallyuniform cross section and arranged in vertical and horizontal rows whenviewed in elevation of a said end face thereof to define a honeycombmatrix; said mask, of flexible elastomeric material, includes a flatbase member of a size and shape complementary to a said end face wherebyit can be placed in abutment thereagainst, said base member having aplurality of equally spaced apart flexible pins extending outward fromone face thereof with said pins arranged in a checkerboardconfiguration, said pins being of a size and shape for insertion intosaid passages, said base having a plurality of equally spaced aperturesextending therethrough with said apertures arranged intermediateadjacent said pins, said apertures being of a size and shape whereby afiller material can be extruded therethrough into the associate alignedalternate passages of the monolith element whereby to effect blocking ofthat end of said passages.